The photo decomposing reaction of water have been interested in from the view point of photo energy transformation. And the photo-catalyst which indicates activity to the photo decomposing reaction can be considered as a high quality photo functional material providing a function such as photo absorption, electrolytic separation or oxidation-reduction reaction at the surface.
The inventors of the present invention already reported that BaTiO4O9 having pentagonal prism shape tunnel structure or M2Ti6O13 (M=Na, K, Rb) having oblong shape tunnel structure can own an excellent activity to the complete decomposing reaction of water. Further, the inventors of the present invention also reported that in the case of this catalyst, the photocatalytic activity changes depend on the temperature at the oxidizing treatment, and in the case of BaTiO4O9, the inner crystalline polarization (increase of dipole moment) caused by incommensurate structure of TiO2 octahedron contributes the high activity.
However, the reported solid photo-catalyst which is useful for the complete photocatalytic decomposing reaction is an oxide of transition metal in d0 configuration and limited to an oxide containing Ti, Zr, Nb and Ta.
The subject of the present invention is to provide a photo-catalyst of novel chemical constitution and structure apart from above mentioned metal oxide.
Aiming to dissolve above mentioned subject, the inventors of the present invention, tried to obtain a novel phosphate photo-catalyst by extending to the phosphate containing a transition metal ion or a typical metallic ion in d10 or d0 configuration. The photo-catalytic activity, in particular, the photo-catalyst for the complete decomposition of water of the compound obtained by calcining the blended product consisting of supplying source for transition metal and typical metal ion, supplying source of alkali metal and supplying source of phosphoric acid by changing the calcination temperature and to which RuO2 is loaded is investigated, and then the dipole moment of the phosphate compound which brings high activity is calculated. Consequently, it becomes clear that the oxygen octahedrally surrounding above mentioned transition or typical metallic ion is becoming more strained structure, and also it becomes clear that the compound having a structure indicating high activity as the photo-catalyst for complete decomposition of water by regulating calcination temperature can be obtained, when RuO2 is loaded, thus the subject of the present invention is accomplished.